Composite organic-inorganic energy harvesting devices and methods

ABSTRACT

A hybrid organic-inorganic thin film is provided. The hybrid organic-inorganic thin film comprising: an organic-phase comprising a porous organic nanostructure comprised of an interpenetrating network having at least one dimension between 0.1 and 100 nm; and an inorganic phase at least partially distributed within the porosity of the organic phase. In a first aspect, the organic phase has a first band gap and the inorganic phase has a second band gap different from the first band gap. A method of producing an organic-inorganic energy harvesting device and a device therefrom comprising the hybrid organic-inorganic thin film is provided.

TECHNICAL FIELD

This disclosure relates to hybrid organic-inorganic energy harvestingdevices based on an inverted manufacturing strategy comprising porousorganic material with inorganic material deposited therein, methods offabrication, and devices therefrom.

BACKGROUND

Strategies currently used to produce hybrid solar cell devices arelimited, in part because they typically produce organic domains that aretoo large (typically >50 nm). This large size results in significantexciton decay before diffusion to p/n interface can occur. Despitecurrently having very low efficiency values, hybrid solar cells couldprove to be one of the most disruptive technologies in the solar-modulemarket because of (1) their very low production cost, (2) theirpotential for long-term stability and (3) their great potential forproducing high efficiency multi-junction devices.

Typically, in the above methodology, a porous inorganic framework issynthesized using a variety of methods and it is subsequently filled, orat least partially filled, with suitable organic components.Unfortunately, inorganic frameworks cannot be produced with poressmaller than typical values for the exciton diffusion length (<10 nm).Furthermore, even if these small pore structures could be fabricated,diffusion and viscous limitations become increasingly severe and blockthe infiltration of the organic material.

The efficiency of previous hybrid cells has remained disappointingly lowand improvements have been incremental and slow. This stark lack ofprogress originates from a fundamental flaw in the way hybrid devicesare produced.

Some current approaches to generating hybrid photovoltaics includetemplated growth of zinc oxide (ZnO) nanowires and subsequentbackfilling with poly(3-hexylthiophene) (P3HT). Devices based on thisapproach have limited applications because of the templating processand, moreover suffer from poor interfacial contact between materialswith reported optimized power conversion efficiencies (PCE) of 2.7% orless. Another reported approach included the mixing of P3HT and ZnOnanoparticles in a single solution for coating from solution. While thisapproach is not limited by processability, it is limited by the randommorphology of the photoactive layer that limits phase interconnectivityand, therefore, has resulted in reported optimized PCE of 2.0% or less.

SUMMARY

In a first embodiment, a method of producing an organic-inorganic energyharvesting device is provided. The method comprising introducing anorganic layer to a conductive substrate, the organic layer comprising aninterpenetrating network having at least one dimension between 0.1 and100 nm; and introducing one or more semiconducting inorganic materialswithin the interpenetrating network. In an aspect of the embodiment, theorganic layer has a first band gap and the one or more inorganicsemiconducting materials have, independently, a second band gapdifferent from the first band gap.

Alone or in combination with any one of the previous aspects, theorganic layer comprises one or more conjugated polymers. The one or moreconjugated polymers can comprise branching and/or roping.

Alone or in combination with any one of the previous aspects, theorganic layer is introduced to the substrate by solvent casting, spincoating, blade coating or spraying. Alone or in combination with any oneof the previous aspects, the organic layer is an organogel of one ormore conjugated polymers.

Alone or in combination with any one of the previous aspects, the one ormore semiconducting inorganic materials are introduced by deposition.Alone or in combination with any one of the previous aspects, the one ormore semiconducting inorganic materials are introduced by plasmaassisted deposition or chemical vapor deposition, atomic layerdeposition, or magnetron sputtering. Alone or in combination with anyone of the previous aspects, the one or more semiconducting inorganicmaterials are introduced directly to the interpenetrating network offibers.

An energy harvesting device formed by any of the above aspects.

In a second embodiment, a hybrid organic-inorganic thin film isprovided. The hybrid organic-inorganic thin film comprising: anorganic-phase comprising a porous organic nanostructure comprised of aninterpenetrating network having at least one dimension between 0.1 and100 nm; and an inorganic phase at least partially distributed within theporosity of the organic phase. In a first aspect, the organic phase hasa first band gap and the inorganic phase has a second band gap differentfrom the first band gap.

Alone or in combination with any one of the previous aspects, theorganic phase comprises one or more conjugated polymers, the one or moreconjugated polymers comprises branching and/or roping. Alone or incombination with any one of the previous aspects, the organic layer isan organogel of one or more conjugated polymers.

Alone or in combination with any one of the previous aspects, theinorganic phase comprises one or more semiconducting inorganicmaterials. Alone or in combination with any one of the previous aspects,the one or more semiconducting inorganic materials are dispersed ordistributed among the interpenetrating network of fibers.

In a third embodiment, a hybrid organic-inorganic energy harvestingdevice is provided. The hybrid organic-inorganic energy harvestingdevice comprising: a first electrode; an organic layer deposited on thefirst electrode, the organic layer comprising an interpenetratingnetwork of one or more conjugated polymer fibers having at least onedimension between 0.1 and 100 nm to the substrate; and an inorganicsemiconducting material at least partially distributed within theinterpenetrating network of fibers; and a second electrode, wherein theorganic layer and the inorganic semiconducting material are sandwichedbetween the first and the second electrodes. The organic layer can be anorganogel of one or more conjugated polymers.

Alone or in combination with any one of the previous aspects, theorganic layer is an organogel of the one or more conjugated polymers.

Alone or in combination with any one of the previous aspects, theorganic phase in is an organogel of one or more conjugated polymershaving a first band gap and the inorganic phase has a second band gapdifferent from the first band gap. The device can be a solar cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exemplary method for producing hybrid solar celldevices by conformably coating an inorganic semiconductor phase around aself-assembled organic fiber network disclosed herein.

FIG. 2 depicts a Transmission Electron Micrograph (TEM) of a thin-filmorganic fiber network of poly-3-hexyl-thiophene (P3HT) coated from anorganic solvent.

FIG. 3 depicts an enlarged section of FIG. 2 showing a nucleationcenter.

FIG. 4 an enlarged section of FIG. 2 showing a branching point.

FIG. 5 depicts an enlarged section of FIG. 2 showing roping.

FIG. 6 is a Scanning Electron Microscope (SEM) of a multilayer coatingof thin-film organic fiber network and semiconducting metal oxide on asubstrate.

FIG. 7 is a current-voltage plot of an exemplary energy harvestingdevice as disclosed herein.

FIG. 8 is a current-voltage plot of an exemplary energy harvestingdevice as disclosed herein.

DETAILED DESCRIPTION

The present disclosure describes the formation of composite films thatcan be used for the manufacture of electronic devices (e.g. solar cells,transistors, or light emitting diodes). These composite films willcomprise two interconnected phases of different materials. In oneaspect, the composite film comprises an organic-inorganic interconnectedphase. In one aspect, one phase is provided by solution or solvent-basedmethods and the other phase is provided by a deposition method.Combining solution and plasma methods allows the formation of p/njunctions with ideal properties (e.g., high interfacial area and chargeconnectivity). It also allows utilization of highly complex chemistriesthat are compatible with deposition but not with solvent depositionmethods, and vise-versa.

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the present disclosure are shown, which are embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the claims to those skilled in the art. Like numbersrefer to like elements throughout.

Definitions

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “deposited on” or “deposited onto”another element, it can be directly deposited on or deposited onto theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly deposited on” or“directly deposited onto” another element, there are no interveningelements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” or “top” or “bottom” may be used herein todescribe a relationship of one element, layer or region to anotherelement, layer or region as illustrated in the figures. It will beunderstood that these terms are intended to encompass differentorientations of the device in addition to the orientation depicted inthe figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” “comprising,” “includes” and/or “including” when usedherein, specify the presence of stated features, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, steps, operations, elements,components, and/or combinations thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

Unless otherwise expressly stated, comparative, quantitative terms suchas “less” and “greater”, are intended to encompass the concept ofequality. As an example, “less” can mean not only “less” in thestrictest mathematical sense, but also, “less than or equal to.”

The term “organogel” is inclusive of any solid or semi-solid porousmaterial, partially or substantially crystalline and/or amorphous,having an organic phase of self-assembled mono- or multilayers ofstructured molecules or polymers organized in such a way that they forma three-dimensional network structure or interpenetrating networkstructure of fibers, polymer fibers, individual molecules, polymerchains, or combinations thereof. Structured molecules or polymersinclude small molecule semiconductors and conjugated polymers. The poresof the three-dimensional network structure may or may contain a solventor liquid material. The three-dimensional network of the organogel canbe cross-linked. Cross-linking can be physical (e.g., entanglement) orchemical (covalent or ionic).

The phrase “interfacial area” as used herein is inclusive of a surfacearea of interconnection and/or contact between organic and inorganicmaterials or phases. The interfacial area includes surface area ofinterconnection and/or contact between inorganic material used to fillthe interstitial space of the organic material. The interface includes,for example, the conjunction between the interstitial space of aconjugated polymer (e.g., polymer fibers) and the inorganic materialpresent therein. The interfacial area is also inclusive of an areadefining the two contacting phases. The total density of interfacialarea present is between about 1 meter squared (m²)/milliliter totalcomposite film volume (grams/density) to about 200 m²/milliliter oftotal composite film volume, which includes all organic and inorganicmaterials present in the interstitial space. A typical value for adispersion of TiO₂ nanorods or particles is about 200 m²/g, while anordered (grown) nanotube/rod array can be about 1 m²/g) depending on thesurface density.

The term “porous” is used herein and is inclusive of a low bulk densitymaterial of solid or semi-solid material, partially or substantiallycrystalline and/or amorphous material having a plurality of voids. Inone aspect, the voids have an average void diameter of approximately 100nm but the pore size is approximately 10 nm to 10 μm. A porous organogelmaterial e.g., comprising conjugated polymer, has a relatively highinterfacial area when subjected to the solution/solvent depositionmethods as disclosed herein in part due to concentrated samples,however, it is assumed that the void size is the same as thecharacteristic spacing between nanofibers or other void-like structurein the interpenetrating network.

The term “percolated” is inclusive of a porous organic material, organicpolymer, conjugated organic polymer, and/or organogel in which domainsare interconnected after processing, in accordance with the methodsdisclosed herein, so as to contain an inorganic material positionedand/or distributed within at least a portion of a void or void space ofthe porous organic material.

The terms “fiber” and “fibrillar” are used herein interchangeably.

The term “substantially” as used herein is inclusive of an amountgreater than 80%, greater than 85%, greater than 90%, greater than 95%,up to 100%. For example, substantially crystalline is inclusive of anamount of crystallinity between 80% and 100%.

The term “about” as used herein is inclusive of +/−10%, +/−7%, +/−5%,+/−3%, +/−2% or +/−1% of the stated value unless otherwise indicated.

The phrase “conjugated polymer” as used herein is given its ordinary andcustomary meaning and is inclusive of polymer systems, and/or oligomericsystems, capable of conducting electric charge, with or withoutadditional compounds, dopants, etc. While not conjugated polymers, perse, small-molecule dyes possessing semiconducting properties can also beused.

The inverted method disclosed and described herein provides hybridactive layers that most excitons generated within the organic phase ofthe dual phase organic-inorganic structure will diffuse to a p/njunction before recombination occurs and provide for the efficientseparation and collection of charges.

Organic Materials and Polymers

Organogels of conjugated molecules, polymers or small-molecule dyes,formed through controlled self-assembly after deposition usingsolution-based coating methods are provided. The present approach isgenerally applicable to organic materials and polymers with tunableband-gaps and optical absorption spectra. In one aspect, conjugatedpolymers are employed. The organic material or polymers can be depositedon the substrate using a variety of methods such as screen printing, orspray, blade, or spin coating.

Exemplary conjugated polymers include:

Where P3HT is poly(3-hexylthiophene-2,5-diyl); P3OT ispoly(3-octylthiophene-2,5-diyl); P3DDT ispoly(3-dodecylthiophene-2,5-diyl); and PFO is poly(9,9-dioctyl fluorene.Other conjugated polymers and materials can be used in spirit and scopeof the present disclosure. Other materials include acceptors and/ordonors capable of adjusting HOMO and LUMO levels of the system, namelyorganic/inorganic interfaces.

In one aspect, the conjugated polymer is prepared such that a porousstructure, which is inclusive of an interpenetrating fiber network, isprovided. In one example, the conjugated organic polymer is dissolved ina solvent, cooled rapidly, and allowed to gel. In one aspect, theconjugated organic polymer dissolved in a solvent and cooled rapidlyprovides an organogel. In one aspect, the organogel comprises aninterpenetrating network of conjugated polymer fibers. Theinterpenetrating network of conjugated polymer fibers can provide adefined fiber structure (organic phase organic domain). In one aspect,the fiber structure is formed from multiple polymer chains that arestacked together due to specific interactions between pi orbitals in amechanism that is also known as “pi-pi” stacking. The inter-penetratingnetwork of conjugated polymer fibers can comprise covalently ornon-covalently coupled fibers. The covalently or non-covalently coupledfibers can be branched, linear, or combinations thereof, covalently orionically cross-linked or substantially non-cross-linked.

Inorganic Materials

Exemplary inorganic materials include inorganic oxides, inorganiccarbides, or inorganic nitrides, sulfides, for example,oxides/nitrides/sulfides/carbides of boron, titanium, zinc, iron,tungsten, vanadium, aluminum, niobium, oxides of silver, oxides ofcopper, oxides of tin, and mixtures thereof. In certain aspects, theinorganic materials are semiconductors. The oxides listed above includesub-oxides, stoichiometric oxides, and super-oxides, and includes,without limitation, one or more of TiO₂, ZnO, Fe₂O₃, WO₃, SnO₂, Al₂O₃,V₂O₃, MoO₃, NiO, SrTiO₃, as well as cesium carbonate Cs(CO₃), aluminumnitride (AlN), and boron nitride (BN). The one or more of inorganicoxide, inorganic carbide, or inorganic nitrides can be used in a formthat is suitable for deposition. The one or more of inorganic oxide,inorganic carbide, or inorganic nitrides can be of a size or formsuitable for such applications, including powders, micron particles,submicron particles, nanoparticles, and physical mixtures and/ordistributions thereof. Organometallic precursor compounds can be usedalone or in combination with other reactants/precursors to introduce tothe organic material, in-situ, and/or the formation of the inorganicmaterial. Non-limiting examples of organometallic precursors includemetal alkyls, metal hydrides, metal carboxylates, metalcyclopentadienyls, metal carbonyls, and combinations.

Deposition Techniques

The organic material discussed above can be deposited using conventionaltechniques, e.g., solvent casting, spin coating, blade coating, dropcasting, screen printing, etc., which can be followed, as needed, byevaporative methods to remove substantially all of the solvent.Techniques to provide the porosity include conventional methods as wellas those disclosed herein. Suitable substrates for the organic material,if used, include conductive substrates, metals, metal-coated polymerfilms, semiconducting thin films, e.g., ITO and the like. The substratecan be rigid or flexible.

The inorganic material can be coated conformably around the above porousorganic framework, using one or more deposition processes, to provide apercolated thin film comprising a porous organic material with inorganicmaterial deposited with the pores or voids of the organic material. Inone aspect, a networked organic phase comprising suitably sized porousdomains is produced via solution or solvent-based methods, e.g., oforganogels, in combination with one or more deposition methods thatsubsequently forms pore-filling inorganic phases. The inorganic phase isat least partially positioned within the organic phase and provides atleast a dual phase having interfacial contact between the phases. In oneaspect the deposition process is chosen so as to minimize undesirablethermal effects to the organic phase, such as melting or other inducedphase transitions, degradation, crosslinking, etc.

Exemplary examples of deposition processes for the inorganic materialsthat may be utilized in carrying out the methods herein disclosedinclude; simple vacuum evaporative deposition, low-temperature chemicalvapor deposition (CVD); atomic layer deposition (ALD); corona discharge;dielectric barrier discharge; atmospheric pressure plasma jet; plasmaenhanced chemical vapor deposition; atmospheric plasma glow discharge;atmospheric-pressure plasma liquid deposition; and magnetron sputtering.In one aspect, one or more of an evaporative deposition, a plasma orplasma-assisted deposition, chemical vapor deposition (CVD), metalorganic chemical deposition (MOCVD), sputtering deposition, e.g.,magnetron, is utilized to introduce, e.g., by depositing on or in, ordepositing directly on or in, conformal inorganic material to porousregions of an organic material. Metals, metal oxides, metal carbides,metal sulfides, etc., can be deposited. In specific aspects of theembodiments herein disclosed, a deposition technology is utilized todeposit inorganic material on a conjugated polymer to provide anorganic-inorganic energy harvesting device.

Energy Harvesting Devices

Hybrid energy harvesting devices can be produced with the presentinverted method herein disclosed with low production costs, in partbecause they constitute a thin-film technology with low materialrequirements and because they use abundant raw materials (e.g.,metal-oxides and organic compounds). Deposition methods are compatiblewith scalable manufacturing processes (e.g., roll-to-roll). Hybrid solarcells prepared by the methods disclosed herein take advantage of thehighly tunable electronic structure of conjugated organic materials.This allows for the synthesis of the presently disclosed materials withvariable optical band gaps that can absorb in different regions of thesolar spectrum. Uses for presently disclosed thin film/deposition methodinclude post-production application of photovoltaic coatings underatmospheric conditions.

Thus, in one embodiment, hybrid photovoltaic devices as disclosed hereincomprise a p-type conjugated polymer or material and an n-type inorganicsemiconductor, the p-type conjugated polymer or material and the n-typeinorganic semiconductor having high interfacial contact area andvertical phase interconnectivity sandwiched between electrodes. Theelectrodes can independently be ITOs and/or metallic electrodes,graphene, and/or other conductive materials such as metal oxides, e.g.,ZnO (doped or undoped), conductive ink/pastes, etc. In one aspect theorganic phase comprises conjugated polymers and functions as a p-typesemiconductor and the inorganic phase comprises semiconductor materialthat functions as an n-type semiconductor, the combined phasescomprising a single layer or a plurality of layers. In one aspect, theorganic material is percolated conjugated polymer. In another aspect,the organic material is a percolated conjugated polymer and theinorganic material is a semiconducting metal and/or metal oxide,nitride, sulfide, carbide, etc. Such arrangements of porous inorganicphases and conformal inorganic coatings provide an organic-inorganichybrid composite material with high specific surface area and smallorganic domain sizes.

The use of the presently disclosed deposition process provides for anorganic-inorganic hybrid energy harvesting thin-film. In one example,the organic-inorganic hybrid energy harvesting thin-film is positionedbetween conductive electrodes to provide an energy harvesting device. Inone example the energy harvesting device is a photovoltaic device. Thephotovoltaic device can be a hybrid solar cell. In one aspect, hybridphotovoltaic devices are fabricated using a plasma enhanced depositiontechnology to deposit ZnO films as a conformal material on or directlyon a solution processed, percolated P3HT layer.

Hybrid energy harvesting devices, e.g. solar cells, produced with thepresently disclosed method can likely achieve efficiencies exceeding theShockley-Queisser limit for single-junction devices (PCE greater than33.7%). Hybrid solar cells prepared using the methods disclosed hereinare likely to provide improved power conversion efficiencies (PCE) ofabout 2% to about 10%, to about 20%, to about 30% or more of the currentmaximum attainable values for hybrid solar cells prepared solely fromorganic materials or solely from metal-oxide materials, which have PCEvalues of less than 2%. In addition, unlike fully-organic solar cells,hybrid inorganic-organic solar cells prepared by the method hereindisclosed are likely to have superior environmental stability, in partbecause their inorganic components impart superior mechanical strength,UV protection and improved resiliency to extreme temperatures. Long-termoperational stability of solar modules is advantageous as well as moduleinstallation capability. Hybrid organic-inorganic solar cells asdisclosed herein likely have, and are expected to provide, superioradvantages in this area.

With reference to FIG. 1, an exemplary method is depicted to provide ahybrid organic-inorganic energy harvesting device. Thus, aninterconnected network of nanometer sized organic interconnected fiber20 (e.g., fibers 22 with high specific surface area) is solutiondeposited onto a bottom electrode 10, which may be a substrate,providing an organic phase 24. Inorganic material, preferably asemiconducting material 32, is then deposited on or directly on theorganic phase 24 to backfill the percolated, interconnected networkedfiber layer structure of organic phase 24. Deposition can be for exampleby plasma enhanced deposition techniques, atmospheric plasma techniques,etc. The organic-inorganic phases are sandwiched between top electrode40. The presently disclosed method provides for increased and/orenhanced phase interconnectivity between the electrodes and highinterfacial contact area between the organic and inorganic phases so asto maximize the PCE of the device.

Aerospace vehicles have a unique opportunity to harvest photovoltaicenergy because they are often in direct contact with sunlight, which hasan average power density of 1.2 kW/m². Smaller aircraft that arelightweight and require less fuel and could benefit from this directsource of power. Larger airliners may also benefit from solar energyharvesting for local power needs such as electro-chromic windowassemblies or structural health monitoring systems (SHM) sensors.Low-cost alternative power sources will likely play a role incontributing to the total power load of future vehicles and systems.Energy harvesting thin-film methods and devices as disclosed herein areconfigurable for implementation on aerospace vehicles because saidmaterials are lightweight and low-cost. In addition, energy harvestingthin-film methods and devices as disclosed herein allow conformaldeposition onto parts with a variety of form factors while stillremaining very thin (<1000 nm). The methods and devices disclosed hereinprovide for efficiency enhancement of hybrid photovoltaics andprocessing advantages that would allow for their direct application onfuture aircraft components.

In a first example, spin cast fibrillar poly(3-hexylthiophenes) and zincoxide are provided. The morphology of both layers is independentlyconfigured for interconnectivity and high interfacial contact in orderto maximize device efficiency. Examples of organogel thin films withdifferent optical, structural and electrical properties were preparedand evaluated with various inorganic semiconductor materials depositedusing vapor deposition techniques.

Regioregular poly(3-hexylthiophene) was purchased from Rieke metals andwas reported to have a regioregularity, molecular weight andpolydispersity index (PDI) of 93%, 41000 g/mol and 2.0, respectively.The P3HT was dissolved in toluene (purity >99.5%) at a highconcentrations (>5 mg/mL) and at elevated temperatures (>80° C.) to forma completely dissolved polymer solution. Self-assembly and gelation wasthen induced through rapid cooling to approximately 5° C. in therefrigerator to percolated fiber networks.

As shown in FIG. 2, fibrillar poly(3-hexylthiophene) networks of nano-or sub-micron to micron dimensions were generated at concentrations of5, 10, 20 and 30 mg/mL and were deposited via spin-coating onto glasscover slips. FIG. 3 depicts a Transmission Electron Micrograph (TEM) ofthe thin-film organic fiber network of poly-3-hexyl-thiophene (P3HT),showing nucleation center 50, which is further depicted in exploded viewFIG. 3. Additional morphology is demonstrated in enlarged sectionsdepicted in FIGS. 4, 5, showing a branching point 60 and roping 70. Theformation of interconnected fiber networks like the one shown in FIG. 2is common to most conjugated organic materials due to their tendency toform pi-pi stacked fiber structures.

Concentration of the P3HT solution can be varied to provide a lessporous network structure. Four spin speeds (1000, 1400, 1800 and 2200RPM) and three deposition volumes (0.25 mL, 0.5 mL and 2×0.25 mL) wereutilized to modify: the exciton bandwidth, which characterizes thedegree of disorder within a crystalline P3HT fiber; the filmconductivity, which characterizes how efficiently charges can be passedthrough the network structure; the fractional absorbance, whichdetermines the maximum light that can be converted to current; and thefilm roughness, which describes the likelihood of pinhole defects.

Small angle x-ray scattering (SAXS) profiles for P3HT organogels formedin toluene and fibers present therein were found to be approximately 5nm in thickness and 17 nm in width, which are ideal for exciton (boundelectron-hole pairs) diffusion. As a result, the P3HT organogels areuseful for p-type/n-type interface diffusion of excitons when used inhybrid photovoltaic devices. It is generally known that excitons have amaximum diffusion length of approximately 10 nm, which corresponds tothe dimensions of the presently prepared P3HT fibers as within the idealrange for exciton diffusion. Furthermore, the P3HT fibers are notlaterally aggregated in solution prior to film deposition and the P3HTfibers do not laterally aggregate during drying based on SAXS profilesfor a P3HT fiber solution and a dried thin film generated from that samesolution. As a result, small exciton diffusion distances and an overallincrease in the potential p-type/n-type interfacial area is obtained.

Exciton bandwidth, which is a quantitative value for the crystallineordering of P3HT fibers, was found to be constant regardless of P3HTsolution concentration. Experiments demonstrated that the thin filmconductivity (proportional to hole mobility) varies as a function ofconcentration for films prepared by the method. While not to be held byany particular theory, it is believed that while the electronicstructure of the P3HT fibers is equivalent, the interconnectivity (e.g.,network structure) of that particular sample is not. Higherconcentration P3HT gels provide a more interconnected network structuredue to the higher fiber density. A single absorbance value can becalculated when the wavelength-dependent thin film absorbance isweighted by the solar spectrum and summed across all visiblewavelengths. Since light absorption is dominated by the thickness and/orconcentration of the conjugated polymer in the presently disclosedP3HT/ZnO hybrid photovoltaic devices, this parameter is optimized.

High concentrations of conjugated polymer can lead to substantialincreases in film roughness, which in certain aspects is an undesirabletrait for photovoltaic devices because it can lead to pin-hole shortcircuits. It is observed that while concentration of the P3HT films hasa substantial effect on the thin film structural, optical and electricalproperties, solution processing of the P3HT films does not have asignificant effect on these properties.

Substrates for coating, typically glass slides, were cleaned prior todeposition of the above P3HT utilizing the following sequential fifteenminute sonication steps: soapy water, DI water, acetone and ethanol. Thesubstrates were then exposed to air plasma using a March Plasmod GCM-200device operating at 150 W and 0.2 Torr for five minutes. For devicepreparation, substrates were coated with 1 mL ofpoly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) PEDOT:PSS;Clevios 1000) at 1500 RPM for 1 minute and then baked at 150° C. for 5minutes, then the P3HT organogel solution was spin coated on top of thePEDOT:PSS film at 1500 RPM for 1 minute. All solution coating steps wereperformed in air.

Zinc Oxide Inorganic Deposition

ZnO was magnetron sputtered on the above P3HT organogel thin film andproperties of the resultant metal oxide-conjugated organic polymercomposite film was evaluated. Zinc oxide was deposited using magnetronsputtering at a thickness of 50-250 nm under the following depositionconditions: pressure=10 mtorr, power=50 W and deposition rate=2 Å/s, DCbias=−108, argon flow=188 sccm and rotation=5. FIG. 6 depicts an SEMimage of an exemplary sample having a 100 nm P3HT organogel film coatedwith 100 nm of ZnO via magnetron sputtering. FIG. 6 shows ZnO depositeddirectly on the porous P3HT network structure. The image indicates twodistinct phases that are not likely completely interpenetrating, butnonetheless contain a substantial amount of bi-layer conformation withinan interpenetrating region at the interface between the two layers.Modification of this bi-layer structure to maximize the phaseinterconnectivity of the high surface area of the fibers present in theorganic phase optimizes overall device efficiency. Further optimizationcan be realized by maximizing crystallinity of the inorganic phase, forexample.

Band energy alignment for hybrid photovoltaic devices based on aP3HT/ZnO photoactive layer was found to be significantly different thanthat reported in literature, likely, at least in part, due to theamorphous in nature of the inorganic oxide film. Low temperaturedeposition processes that avoid thermal degradation of the P3HT film,such as magnetron sputtering, typically provide amorphous films leadingto a slight band gap mismatch and some energetic barriers to excitondissociation that lower the overall device efficiency.

The degradation of a P3HT film after exposure to plasma wasinvestigated. Thus, a P3HT organogel thin film was exposed toatmospheric plasma at a power 80 W for 2 minutes and at a distance of 5mm. After this exposure, a 20% decrease in the electrical conductivitywas measured, suggesting that the P3HT film may degrade in the presenceof high energy plasma. On the other hand, a P3HT organogel and a P3HTorganogel coated with zinc oxide using magnetron sputtering were foundto have very similar optical properties, except at low wavelength whereZnO absorbs light, which suggests that the electronic band structure isnot appreciably degrading with the magnetron sputtering depositiontechnique.

Strontium Titanate Inorganic Deposition Example

As discussed above, there are many organic and inorganic materialcombinations that can be utilized to provide the instant hybrid energyharvesting thin film devices in addition to the exemplary ZnO/P3HT-baseddevice disclosed above. The purpose of this example was to evaluate theperformance of a non-equal band structure pairing hybrid inorganic-inorganic energy harvesting device. Strontium titanate has awider band gap than ZnO and therefore the band mismatch will be greater.SrTiO₃ is known to crystallize at very high temperature (>450° C.) andtherefore it is likely that this material is also deposited as anamorphous oxide. Thus, a P3HT/SrTiO₃-based device was prepared in asimilar manner and in accordance with the methods disclosed herein.Strontium titanate was deposited on glass using magnetron sputtering atthickness of 50-250 nm under the following deposition conditions:pressure=3.2×10⁻⁷ torr, power=14% and deposition rate=2 Å/s, and theelectronic band structure was characterized using a combination ofUV-Vis spectroscopy and x-ray photoelectron spectroscopy (XPS).

Device Preparation

Hybrid thin film photovoltaics were generated using an inverted devicegeometry process comprising the structure of: ITO/PEDOT:PSS/P3HT/ZnO/Al.Thus, 1″×1″ ITO coated glass is cleaned by sonication in soapy water, DIwater, acetone and ethanol for 15 minutes each. The slides are thendried using lab air and placed in an air plasma (pressure=0.2 torr andpower=150 W) for 5 minutes to increase the wetting of the next step.Clevios 1000; poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) was utilized as a hole transport layer, which was filteredthrough a 450 μm filter prior to deposition. One milliliter of PEDOT:PSSsolution was then spin-coated on top of the ITO with a “wetting” step of650 RPM for 10 minutes followed by a “evaporation” step of 1500 RPM for60 seconds. The PEDOT:PSS film was then annealed to remove trace waterat 150° C. for 5 minutes. The P3HT/metal oxide active layer is thendeposited as described above. An aluminum electrode is deposited usingthermal evaporation with a shadow mask to define the device size (25 mmin diameter) and generate multiple devices (9×) per sample. Finally,conductive epoxy is utilized to create a bridge between the aluminumelectrode and a metal wire for device testing.

Device Testing

Photovoltaic device properties of the samples prepared as describedabove were tested by connecting the ITO and aluminum electrodes to aKeithley 2400. Devices were held perpendicular to the incident light andat a pre-calibrated distance to generate a standard “1 sun” measurement.The “1 sun” condition was confirmed using a silicon solar cell standard.Voltage sweeps of 201 points over a −1 to 1 V range with a delay of 1second per measurement were performed. Efficiency (η) and fill factor(FF) were calculated using literature methods.

FIG. 7 depicts the current-voltage (I-V) characteristics for theexemplary P3HT/ZnO device prepared by the method disclosed herein. Fromthis characteristic I-V curve the short circuit current (Jsc) and opencircuit voltage (Voc) can be determined and utilized to calculate thefill factor (FF) and overall efficiency (η) of the device. From theexperimental data depicted in FIG. 7, the maximum Voc, FF and η forexamples prepared by the present method were found to be 0.45 V, 43% and0.002%, respectively. The Voc and FF are comparable with reportedmeasurements for P3HT/ZnO devices prepared by previously reportedmethods. The observed extractable current of the presently discloseddevices are low, however, modification of the process and the materialprepared therefrom provided increases in device efficiency of as much astwo orders of magnitude, and suggests that these exemplary devices haveformed a bi-layer structure, in which exciton dissociation likely occurspredominantly at the thin P3HT/ZnO interface. These results demonstratethat minimizing the bilayer structure and maximizing the inorganicmaterial penetration within the organic fiber network will increasedevice efficiency Thus, the presently disclosed method demonstrates thatfunctional energy harvesting devices can be generated using asolution-coated fibrillar, percolated P3HT network as the organic phasehaving ZnO deposited on or directly on the percolated network. Forexample, when a P3HT/ZnO composite film is sandwiched between twoconductive electrodes a functional photovoltaic device is formed.

Typically, a large band mismatch is not desirable for photovoltaicdevices because it creates energetic barriers for separating charges.Not surprisingly, therefore, the device performance for the P3HT/SrTiO₃sample prepared by the methods disclosed above was less than P3HT/ZnOdevices prepared as described above. FIG. 8 depicts the dark and lightcurrent-voltage response for the P3HT/SrTiO₃ photovoltaic deviceprepared by the present method under “1 sun” conditions. Surprisinglyhowever, the open circuit voltage (Voc) for P3HT/SrTiO₃ is extremelyhigh for the P3HT/ZnO-based device, being observed at 1.1 V, which issignificantly higher than reported optimized literature values. Thisdata demonstrates that utilizing thin, mismatched energetic layersprovides a surprising increase of the Voc of hybrid photovoltaicdevices.

Batch/Semi-Batch/Continuous Processing

The instantly described process may be configured and design to operateas a batch process, for example, organogel films can be fabricatedseparately, followed by a subsequent inorganic material coating process.

Alternatively, the instantly described apparatus and/or process may becontinuous, the method including a step of continuously casting and/orcoating a substrate with the organic polymer organogel films anddepositing the inorganic material.

From the foregoing description, various modifications and changes in thecompositions and method will occur to those skilled in the art withoutvarying from the scope of the invention as defined in the followingclaims.

What is claimed:
 1. A hybrid organic-inorganic thin film comprising: an organic-phase comprising a porous organic nanostructure comprised of an interpenetrating network of one or more conjugated polymer fibers, the network having a plurality of voids of dimension between 0.1 and 100 nm, wherein the one or more conjugated polymer fibers comprises branching and/or roping; and an amorphous inorganic phase at least partially distributed within the plurality of voids of the organic phase.
 2. A hybrid organic-inorganic thin film of claim 1, wherein the organic phase has a first band gap and the inorganic phase has a second band gap different from the first band gap.
 3. A hybrid organic-inorganic thin film of claim 1, wherein the organic layer is an organogel of one or more conjugated polymer fibers.
 4. A hybrid organic-inorganic thin film of claim 1, wherein the inorganic phase comprises one or more semiconducting inorganic materials.
 5. A hybrid organic-inorganic thin film of claim 4, wherein the one or more semiconducting inorganic materials are dispersed or distributed within the plurality of voids of the interpenetrating network.
 6. A hybrid organic-inorganic thin film of claim 1, wherein the interpenetrating network is poly (3-hexylthiophene-2,5-diyl); poly(3-octylthiophene-2,5-diyl); poly(3-dodecylthiophene-2,5-diyl); or poly(9,9-dioctyl fluorene).
 7. A hybrid organic-inorganic thin film of claim 1, wherein the interpenetrating network is poly (3-hexylthiophene-2,5-diyl); poly(3-octylthiophene-2,5-diyl); poly(3-dodecylthiophene-2,5-diyl); or poly(9,9-dioctyl fluorene) and the inorganic phase is TiO₂, ZnO, Fe₂O₃, WO₃, SnO₂, Al₂O₃, V₂O₃, MoO₃, NiO, SrTiO₃, Cs(CO₃), AlN, or BN.
 8. A hybrid organic-inorganic thin film of claim 1, wherein the interpenetrating network is poly (3-hexylthiophene-2,5-diyl) fibers and the inorganic phase is plasma deposited TiO₂ or SrTiO₃.
 9. A hybrid organic-inorganic energy harvesting device comprising: a first electrode; an organic layer deposited on the first electrode, the organic layer comprising a porous interpenetrating network of one or more conjugated polymer fibers defining a plurality of voids of dimension between 0.1 and 100 nm to the substrate; and an amorphous inorganic semiconducting material at least partially distributed within the interpenetrating network of fibers; and a second electrode, wherein the organic layer and the inorganic semiconducting material are sandwiched between the first and the second electrodes.
 10. A hybrid organic-inorganic energy harvesting device of claim 9, wherein the organic layer is an organogel of the one or more conjugated polymer fibers.
 11. A hybrid organic-inorganic energy harvesting device of claim 9, wherein the organic layer is an organogel of one or more conjugated polymer fibers having a first band gap and the inorganic semiconducting material has a second band gap different from the first band gap.
 12. A hybrid organic-inorganic energy harvesting device of claim 9, wherein the device is a solar cell.
 13. A hybrid organic-inorganic energy harvesting device of claim 9, wherein the interpenetrating network is poly (3-hexylthiophene-2,5-diyl); poly(3-octylthiophene-2,5-diyl); poly(3-dodecylthiophene-2,5-diyl); or poly(9,9-dioctyl fluorene).
 14. A hybrid organic-inorganic energy harvesting device of claim 9, wherein the interpenetrating network is poly (3-hexylthiophene-2,5-diyl); poly(3-octylthiophene-2,5-diyl); poly(3-dodecylthiophene-2,5-diyl); or poly(9,9-dioctyl fluorene) and the inorganic phase is TiO₂, ZnO, Fe₂O₃, WO₃, SnO₂, Al₂O₃, V₂O₃, MoO₃, NiO, SrTiO₃, Cs(CO₃), AlN, or BN.
 15. A hybrid organic-inorganic energy harvesting device of claim 9, wherein the interpenetrating network is poly (3-hexylthiophene-2,5-diyl) fibers and the inorganic semiconducting material is plasma deposited TiO₂ or SrTiO₃. 